// Copyright (C) 2024 Kumo inc.
// Author: Jeff.li lijippy@163.com
// All rights reserved.
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published
// by the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.
//


#pragma once

#include <merak/core/tsq.h>

namespace merak {

/**
@private
*/
template <typename T>
class Freelist {

  struct Head {
    std::mutex mutex;
    UnboundedTaskQueue<T> queue;
  };

  public:

  Freelist(size_t N) : _heads(N) {}

  void push(size_t w, T item) {
    std::scoped_lock lock(_heads[w].mutex);
    _heads[w].queue.push(item);  
  }

  void push(T item) {
    push(reinterpret_cast<uintptr_t>(item) % _heads.size(), item);
  }

  T steal(size_t w) {
    for(size_t i=0; i<_heads.size(); i++, w=(w+1)%_heads.size()) {
      if(auto item = _heads[w].queue.steal(); item) {
        return item;
      }
    }
    return nullptr;
  }


  bool empty() const {
    for(const auto& q : _heads) {
      if(!q.queue.empty()) {
        return false;
      }
    }
    return true;
  }

  private:
  
  std::vector<Head> _heads;
};


}  // end of namespace merak -----------------------------------------------------
